Fatal error: Call to a member function pull() on null

Socialite::with('facebook')->stateless()->redirect()->getTargetUrl()

$fb_user = Socialite::with('facebook')->user();

Socialite::with('facebook')->stateless()->redirect()->getTargetUrl()

$fb_user = Socialite::with('facebook')->stateless()->user();

<?php

namespace AppHttpControllers;

use AppHttpControllersController;
use IlluminateSupportFacadesHash;
use IlluminateHttpRequest;
use AppUser;
use AppSocialAccount;
use Socialite;

class SocialController extends Controller
{
public function social(Request $request) {

    $provider = $request->input('provider');
    switch($provider){
        case SocialAccount::SERVICE_FACEBOOK:
            $social_user = Socialite::driver(SocialAccount::SERVICE_FACEBOOK)->fields([
                'name',
                'first_name',
                'last_name',
                'email'
            ]);
            break;
        case SocialAccount::SERVICE_GOOGLE:
            $social_user = Socialite::driver(SocialAccount::SERVICE_GOOGLE)
            ->scopes(['profile','email']);
            break;
        default :
            $social_user = null;
    }

    abort_if($social_user == null , 422,'Provider missing');

    $social_user_details = $social_user->userFromToken($request->input('access_token'));

    abort_if($social_user_details == null , 400,'Invalid credentials'); //|| $fb_user->id != $request->input('userID')

    $account = SocialAccount::where("provider_user_id",$social_user_details->id)
            ->where("provider",$provider)
            ->with('user')->first();

    if($account){
        return $this->issueToken($account->user);
    }
    else {
        // create new user and social login if user with social id not found.
        $user = User::where("email",$social_user_details->getEmail())->first();
        if(!$user){
            // create new social login if user already exist.
            $user = new User;
            switch($provider){
                case SocialAccount::SERVICE_FACEBOOK:
                    $user->first_name = $social_user_details->user['first_name'];
                    $user->last_name = $social_user_details->user['last_name'];
                    break;
                case SocialAccount::SERVICE_GOOGLE:
                    $user->first_name = $social_user_details->user['name']['givenName'];
                    $user->last_name = $social_user_details->user['name']['familyName'];
                    break;
                default :
            }
            $user->email = $social_user_details->getEmail();
            $user->username = $social_user_details->getEmail();
            $user->password = Hash::make('social');
            $user->save();
        }
        $social_account = new SocialAccount;
        $social_account->provider = $provider;
        $social_account->provider_user_id = $social_user_details->id;
        $user->social_accounts()->save($social_account);
        return $this->issueToken($user);
    }
}

private function issueToken(User $user) {

    $userToken = $user->token() ?? $user->createToken('socialLogin');

    return [
        "token_type" => "Bearer",
        "access_token" => $userToken->accessToken
    ];
}
}